Finding the optimal vertical distribution: behavioural responses of Daphnia pulicaria to gradients of environmental factors and the presence of fish
Article first published online: 26 SEP 2012
© 2012 Blackwell Publishing Ltd
Volume 57, Issue 12, pages 2514–2525, December 2012
How to Cite
LARSSON, P. and LAMPERT, W. (2012), Finding the optimal vertical distribution: behavioural responses of Daphnia pulicaria to gradients of environmental factors and the presence of fish. Freshwater Biology, 57: 2514–2525. doi: 10.1111/fwb.12024
- Issue published online: 22 OCT 2012
- Article first published online: 26 SEP 2012
- (Manuscript accepted 23 August 2012)
- environmental gradients;
- fitness optimisation;
- vertical distribution
1. The vertical distribution of zooplankton results from active habitat choice aiming to optimise fitness gain in a system of trade-offs.
2. Using large, controlled indoor mesocosms (Plön Plankton Towers), we monitored the behavioural response of Daphnia pulicaria to vertical gradients of temperature, food, oxygen and light, in the presence and absence of fish predation.
3. In the absence of fish, Daphnia distributed as predicted by an ideal ‘free distribution with costs’. If the food was distributed homogeneously, they stayed in the warm epilimnion, while they balanced their time dwelling in epi- and hypolimnion if the food was concentrated in a deep-water maximum.
4. However, oxygen depletion in the hypolimnion, representing an additional cost, prevented Daphnia from completely exploiting the hypolimnetic food maximum. Consequently, the proportion dwelling in the hypolimnion was larger if oxygen was not limiting.
5. Fish predation had an overwhelming effect, driving Daphnia into the hypolimnion under all experimental conditions. If permitted by oxygen availability, Daphnia used the whole hypolimnion, but oxygen depletion reduced their possible habitat to the upper hypolimnion with oxygen concentrations above c. 0.7 mg L−1. As fish were less tolerant of low oxygen, the layer below the thermocline formed a predation refuge for Daphnia.